A multi-channel surround audio system popular these days has 5 to 8 channels, for example, and also includes an amplifier device which controls the audio outputs of those channels and speakers of numbers corresponding to the number of the channels. In order to realize the surround reproduction, it is necessary to position each speaker at an appropriate position and to set the sound pressure level and frequency characteristic of the audio signal to be adapted to the characteristic of each speaker. Therefore, the amplifier device of the surround audio system generally includes an equalizer and an amplifier for each channel.
Also, in order to reproduce a sound field with presence, there has been proposed a method of using reverberation sound of the input signal. For example, in the Patent Reference-1, the reverberation sound signal is generated based on the acoustic signal and the position information of the listener, and the reverberation sound is synthesized with the original signal to be reproduced.    Patent Reference-1: Japanese Patent Application Laid-open under No. 2003-91293